Reproducibility of allergen-induced early and late asthmatic responses

BACKGROUND: Constant-dose allergen inhalation challenges are frequently used to examine the effect of antiasthma drugs on the allergen-induced early and late asthmatic responses. The end-point measurements in such studies are the maximal early and late percent decreases in the forced expiratory volume in 1 second (FEV1). OBJECTIVE: Our purpose was to observe the reproducibility and to determine the sample sizes required for such studies. METHODS: Twenty-eight subjects with allergen-induced early and late responses were studied with two constant-dose allergen challenges separated by 2 to 12 weeks. The early response was measured as the maximum percent decrease in FEV1 during the first 2 hours and the late response as the maximum percent decrease in FEV1 between 3 to 7 hours. RESULTS: The mean +/- SEM early responses were 23.1% +/- 1.0% and 24.7% +/- 2.0%, whereas the mean late responses were 23.3% +/- 2.0% and 24.5% +/- 2.2%. Reproducibility of measurements were such that fewer than eight subjects are required, to show 50% attenuation of either the early or late response (with 90% power). CONCLUSIONS: The method of constant-dose allergen challenge is a sensitive tool for detecting changes in early and late asthmatic responses after the use of antiasthma medication.